The Big Picture: an outline of the concepts covered to date Genes are physical units of hereditary that carry information from one generation to the next 2. Mendel elucidated the following principles regarding the inheritance patterns of genes A. Each diploid individual contains two copies of a given gene B. Each Gene can have different forms called alleles. There are two alleles in a diploid individual The form that is expressed phenotypically in the heterozygote is known as the dominant allele. It is an operational definition C. These copies (alleles) segregate from one another to form gametes. There is a single copy of each gene in a gamete (one allele of a gene in a gamete) D. Different genes assort independently from one another during gamete formation (unless they are on the same chromosome and are linked) 3. The inheritance pattern of genes parallels the behavior of chromosomes at meiosis. This generated the hypothesis that genes reside on chromosomes OR A a B b

The Big Picture 4. Exceptional patterns of chromosome segregation The X/X and X/Y sex chromosomal system produces exceptional segregation patterns because males contain only one copy of X-linked genes Non-disjunction: homologous chromosomes migrate to the same pole during meiosis 5. Exceptional expression (phenotype) patterns: Incomplete dominance, Co-dominance, Lethal alleles 6. Genes that reside close to one another on the same chromosome do not assort independently- linkage +++++exceptions to Mendellian laws at the level of independent assortment of two genes+++++ 7. Occasionally recombination occurs between these linked genes. The higher the frequency of recombination between any two genes, the greater the distance is between them. Recombination frequencies serve as a useful method of mapping genes along a chromosome. No exceptions to Mendellian laws at the level of the gene, but Phenotype ratios are modified

a b c d e f g 10 20 20 15 15 5 This map means that there is a 20% recombination frequency between the genes b and c and a 5% recombination frequency between the genes f and g Genes very far apart on the same chromosome will appear to assort independently How many map units between a and f? a-f = 80 cM What is the recombination freq between a and f? Is it 80%, less than 80%, more than 80%

a b c d e f g 10 20 15 5 a f af P aF R Af R AF P a f A F A F Recombinant/total = 2/4=50% Maximum freq is 50%

The largest distance that can be measured by this technique is 50MU. 50% also indicates NO LINKAGE If two genes are very far apart on the same chromosome, use markers between these genes to more accurately map the genes Therefore when you obtain a recombination frequency of 50% this means that either: the genes are on two different chromosomes OR very far apart on the same chromosome

Ratios A A a x a 3:1 A a a x a 1:1 A b A b a B x a B 9:3:3:1 A b a b a B x a b 1:1:1:1

Chromosomes, genes, alleles, proteins, phenotypes Each chromosome has one DNA molecule Each chromosome has many genes A gene has many forms- alleles - two alleles in a diploid Each allele produces a protein that give rise to a phenotype Different alleles are caused by different changes in the same gene chromosome yellow white Shaven body Forked bristle blanco Many genes Genes on DNA white1 white2